Mobile millimetric wave radar

ABSTRACT

An antenna unit for sending out electromagnetic waves of a millimetric-wave band to outside and receiving the wave reflected from a target, and circuits for signal-processing the reflected wave are equipped as a vehicular millimetric-wave radar device. Antenna patterns are formed on a surface of a multilayer base plate formed of plural stacked layers of dielectric plates and an electroconductive layer interposed between each layer. Circuit wiring patterns and electronic components for signal processing of millimetric waves are disposed on the reverse side. Among all the above-mentioned electronic components, only a millimetric-wave signal oscillator, amplifier, and frequency converter are haused in a hermetically sealed section formed in a localized space on a face of the multilayer base plate. The other electronic components are arranged in a non-hermetically structured condition on a periphery of the hermetically sealed section. The above-mentioned oscillator, amplifier, and frequency converter are hermetically sealed in an inert gas atmosphere, whereas at least part of the other electronic components arranged in a non-hermetically structured condition is protected by resin coating. With this configuration, a compact, thin, and highly accurate millimetric-wave radar device is provided at a low cost.

TECHNICAL FIELD

The present invention relates to a vehicular millimetric-wave radardevice, and more particularly to a mounting structure for aradiofrequency module integrated with an antenna unit.

BACKGROUND ART

The vehicle-mounted types of radar devices that use millimetric waves orother radio waves to measure the distance and relative velocity withrespect to a vehicle running in front have been developed in recentyears. Millimetric waves, in particular, have the advantage that theyreach to a great distance because of their small radio-beam attenuationseven under rainy, foggy, or other unfavorable weather conditions.

As a mounting structure for a millimetric-wave radar device, thefollowing is considered. The device has an antenna base with an antennapattern formed on its surface and a base plate for a signal-processingcircuit. The processing circuit is used for generating milimetric wavesand processing sending/receiving signals, and comprises electroniccomponents and electroconductive wiring pattern. The antenna base andthe base plate are combined into an assembly and are housed in a case.

In prior arts, as a mounting technology of a integrated-type microwavecircuit used for each wireless terminal unit of mobile-stations in amobile wireless communication system, for example, Japanese Patent No.2,840,493 describes as follows. It proposes that an antenna pattern isformed on one side of a multilayer base plate having plates andelectroconductive layers stacked in multilayer structure, and variouselectronic components for sending and receiving signals are mounted onthe other side of the multiplayer base plate.

The former mounting technology of the above-mentioned conventionaltechnologies cannot sufficiently realize miniaturization of the device,since it has been necessary to manufacture the antenna base and theelectronic-component mounting base plate independently and to stack themin multistage form with a space interposed between each stage.

The latter of the conventional technologies allows both sides of themultilayer base plate to be used effectively, and thus makes a compactdevice design realizable. These conventional technologies, however, doesnot describe structures in relation to moisture protection ofradiofrequency circuits for millimetric waves, and the technologies onmanufacture for preventing such problems has been unsolved.

Radiofrequency circuits of the millimetric wave type are particularlyare prone to change in frequency characteristics according to humidity.Moisture protection is therefore important for these circuits.

An object of the present invention is to provide a vehicularmillimetric-wave radar device capable of solving the above problems andrealizing a compact and low-cost design while, at the same, ensuringhigh productivity and high reliability.

DISCLOSURE OF THE INVENTION

To achieve the above object the present invention is basicallyconstructed as follows:

A vehicular millimetric-wave radar device comprises an antenna unit forsending out electromagnetic waves of a millimetric-wave band to outsideand receiving the waves reflected from a target; and a circuit forsignal-processing the reflected waves. The radar device further includesa multilayer base plate formed of a plurality of stacked layers ofdielectric plates and an electroconductive layer interposed between eachlayer. The multilayer base plate has, on one side, an antenna unitformed with a pattern, and on the other side, a circuit wiring pattern,and electronic components for signal processing of millimetric waves.Among the electronic components, a millimetric-wave signal oscillator,an amplifier, and a frequency converter are housed in a hermeticallysealed section formed with a local space on the multilayer base plate.The other electronic components are arranged in a non-hermeticallystructured condition on a periphery of the hermetically sealed section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a millimetric-wave radardevice according to a first embodiment of the present invention;

FIG. 2 is a partly cutaway plane view of the above millimetric-waveradar device;

FIG. 3 is a rear view of an integrated state of the radome and themultilayer base plate of the above embodiment;

FIG. 4 is a longitudinal sectional view of a millimetric-wave radardevice according to a second embodiment of the present invention;

FIG. 5 is a view showing in section a connection state between theradome and multilayer base plate;

FIG. 6 is a partly enlarged sectional view of FIG. 5;

FIG. 7 is a sectional view showing an example of the above multilayerbase plate;

FIG. 8 is an explanatory diagram showing a manufacturing process for themillimetric-wave radar device according to the above embodiment;

FIG. 9 is a diagram showing the principles of operation of themillimetric-wave radar device according to the present invention;

FIG. 10 is a circuit diagram of the millimetric-wave radar device shownin FIG. 9; and

FIGS. 11 and 12 are diagrams showing a mounting scheme for componentsrelated to the millimetric-wave radar device used in the aboveembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is described below on the basisof the accompanying drawings.

First, basic principles of a millimetric-wave radar device according tothe present embodiment are described using FIG. 9.

A millimetric-wave radar device accordingg to the present embodimentemploys a diplex Doppler radar, which is a typical radar.

A modulated-signal generator (modulator) 24 modulates two frequencies f1and f2 generated with an oscillator 201, by means of rectangular-wavemodulation in time-divided system (see FIG. 9(b)). The modulated signalsare sent out from an sendingt antenna 3A. The signals are reflected froma target (e.g., a preceding vehicle) P, and the reflected signals arereceived with a receiving antenna 3B. The frequencies f1 and f2 are setto a range from, e.g., 76 to 77 GHz.

When a relative velocity V exists between the preceding vehicle P andthe radar (own vehicle) 1, Doppler shifts fd1 and fd2 generate in thefrequencies f1 and f2, respectively, and frequencies of the receivedsignals become f1+fd1 and f2+fd2.

The received signals are converted into time-sharing signals of fd1 andfd2 with a mixer 202 constituted by a frequency converter. After theconversion, Doppler signals fd1 and fd2 are extracted via a switchcircuit 211, which operates in synchronization with the modulatedsignals, and low-pass filters 212 and 213, then A/D converted, and inputto a digital signal processor 25.

The phase difference of Δφ=φ1−φ2 between the frequencies f1+fd1 andf2+fd2, and the Doppler signals fd1 and fd2 can be easily calculated bydiscrete Fourier transform (FET).

The distance “d” between the target (preceding vehicle) and the ownvehicle is represented by the following expression:d=C·φ/4π·Δf  [Numerical expression 1]

-   -   where C is a velocity of light (radio propagation rate) and Δf        is f1-f2. The relative velocity “v” between the vehicles is        represented by the following expression:        v=C·fd 1/2 f 1 or C·fd 2/2 f 2  [Numerical expression 2]

The above FET and calculations with the numerical expressions 1 and 2are each performed by digital signal processing.

A block circuit diagram of the above basic principles is shown in FIG.10.

An RF (Radio Frequency) module 20 is an integrated unit constituted bythe oscillator 201 for forming millimetric-waves, the mixer (frequencyconverter) 202 shown in FIG. 9 and a sending/receiving amplifier (notshown in the figure). In the present embodiment, these elements aremodularized using an IC (integrated circuit), and the module is housedas a hermetically sealed structure 45 on one face of a multilayer baseplate 2 (described later).

An analog block 23 is comprised of an RF signal processor (analogsection) 21 and an A/D converter 22. The RF signal processor (analogsection) 21 is comprised of the switch circuit 211, low-pass filters 211and 212 shown in FIG. 9. The Doppler signals fd1 and fd2 are convertedanalog-to-digital signals and then input to a digital signal processor25.

The digital signal processor 25 controls the modulator 24. In addition,the digital signal processor 25 receives a vehicle velocity signal andbrake signal from outer sensors, and then performs a vehicle safetydecision (for example, alarm decision) based on these signals and theaforementioned signals such as the vehicle-to-vehicle distance signaland relative velocity signal etc. After obtaining information based onthe decision, the digital signal processor 25 sends the information to avehicle control unit (external device) 100 by means of serialcommunications (CAN communications: Controlled Area Network). Thereby avehicle-to-vehicle control signal, an alarm signal, and the like aregenerated, depending on particular conditions. When an ignition (IGN)key switch signal 30 is input, power is supplied from a power supply 26of the millimetric-wave radar device 1.

FIG. 1 is a longitudinal sectional view of a mounting structure for themillimetric-wave radar device of the present embodiment.

A multilayer base plate 2 is formed of a plurality of stacked layers ofinorganic materials (dielectric plates) 200, and has anelectroconductive layer 201 interposed between each layer.

On a surface of the multilayer base plate 2, an antenna unit 3 made ofan organic material is formed by pattern printing. The antenna unit 3includes, as shown in FIG. 2, a sending antenna 3A and receiving antenna3B formed in a sectioned condition to constitute a patch antenna on thesurface of the multilayer base plate 2.

On the other side of the multilayer base plate 2, wiring patterns(signal-processing circuit patterns) 35 are each formed of anelectroconductive film, and electronic components for generating amillimetric waves and processing an input/output signal, are alsoprovided.

In addition, in the multilayer base plate 2, via-holes 6 fortransferring a signal are formed by being filled with anelectroconductive material or by electromagnetic coupling. The antennaunit 3 is electrically connected to the signal-processing circuit wiringpatterns 35 via the via-holes 6.

Among the above-mentioned electronic components, the RF module thatincludes the millimetric-wave signal oscillator 201, the mixer(frequency converter) 200 shown in FIG. 9(a) and an amplifier not shownin the figure, is housed within a hermetically sealed section 45including a case 4 and a cover 5. Other electronic components (theelectronic components used in the analog block 23 of FIG. 10, and theelectronic components used in the digital signal processor 25) arearranged in a non-hermetically structured condition on a periphery ofthe hermetically sealed section 45. The hermetically sealed section 45is, for example, formed in a local space in a central vicinity of themultilayer base plate 2 and internally charged with an inert gas such asa nitrogen gas. In general, the case 4 and the cover 5 are both formedof an inorganic material such as a ceramic material. Structurally,however, a metallic material can be used instead of it.

A microcomputer 251 and a high-speed signal-processing DSP (DigitalSignal Processor) 252, both shown in FIG. 1, are for digitallyprocessing an RF signal, and they constitute the digital signalprocessor 25 described above. These electronic components are arrangedoutside the case 4, and are each coated with an organic protection resin9 to ensure protection from moisture and the like.

The multilayer base plate 2 equipped with the above-mentioned antennaunit and electronic components is covered with a plastic radome (radardome) 7 that improves the passage of electromagnetic wave, and with ametallic case 8 that does not permit easy entry of noise or otherexternal signals.

The radome 7 mechanically protects antenna patterns 3. Distance (designgap) “d” between the inner surface of the radome 7 and the face of theantenna unit side of the multilayer base plate 2 is set to an integermultiple of the wavelength of a millimetric wave. The reason is thatsetting the distance “d” to an integer multiple of one wavelengthreduces millimetric wave (output signal) reflections and thus minimizessignal loss. For example, if the frequency of the millimetric waves isfrom 76 to 77 GHz, the length of one wave is from 3.90 to 3.95 mm.Therefore, the distance “d” is equal to [(3.90 to 3.95)×N], where N isan integer multiple.

The RF module 20, the microcomputer 251, and the DSP 252, each providedon the surface of multilayer base plate 100, are protected from externalradio noise waves by being covered with the above-mentioned metallic(electroconductive) case 8. The case 8, although formed basically of ametallic material, may be of a plastic material having a conductivematerial formed by plating or sputtering.

The RF module (IC chip) 20, microcomputer 251, and DSP 252 in thepresent embodiment are, as shown in FIG. 11, electrically connected bymeans of a face-down scheme, i.e., with an electrode side facingdownward, to form bare chips via the wiring patterns 35 and solder 80existing on the multilayer base plate 2. Alternatively, as shown in FIG.12, the RF module 20, the microcomputer 251 and the DSP 252 may beelectrically connected to the wiring patterns 35 on the multilayer baseplate 2 via a wire-bonding element 81 by means of a face-up scheme,i.e., with an electrode side facing upward. Adoption of such a face-downor face-up mounting structure can assists to reduce the thickness of thedevice.

The layout of the electronic components of the millimetric-wave radardevice in FIG. 1 is shown in FIG. 3.

On one side (reverse side) of the multilayer base plate 2, thehermetically sealed section 45 are located at the central position, onthe other hand, the microcomputer 251, DSP 252, a custom IC 11, a powerMOSIC 12, a power supply regulator 13, an operational amplifier 14, anA/D and D/A converter 15, chip resistors 36, chip capacitors 37 and chipdiodes 38, etc are arranged around the hermetically sealed section.

The radome 7 is bonded with the multilayer base plate 2 to form astructure integrated therewith. The best example of this bondedstructure is described later using FIGS. 5 and 6.

At both sides of the radome 7, an overhang portion 72 protrudingoutwardly with respect to the case 8 is formed, and a plurality ofinstallation holes 72 for installing the millimetric-wave radar device 1at a required section are provided in both overhang portions 72. Bycoupling the radome 7 directly to the multilayer base plate 2, itbecomes easy to get the dimension “d” between the surface of themultilayer base plate 2 and an inner surface of the radome 7 (it is easyto keep a parallel clearance between them by means of the dimension “d”)during the manufacturing process for the device. Also, since theintegrated unit formed of the radome 7 and the multilayer base plate 2can be installed so as to face in a required direction withoutinterposing other members. It is possible to eliminate factors likely tocause dimensional errors in other members, and thus to install theantenna unit 3 accurately. These structure schemes can therefore improvesending/receiving sensitivity. After the radome 7 and the multilayerbase plate 2 have been bonded, the case 8 is bonded with the radome 7and/or the multilayer base plate 2.

Here, the best example of a bonded structure between the multilayer baseplate 2 and the radome 7 is described using FIGS. 5 and 6.

At an inner edge of an opening of the radome 7 is formed an engagementportion 74 that engages with a peripheral edge of the multilayer baseplate 2. The engagement portion 74 is formed with a first face 74 aoriented towards the face of the antenna unit side on the multilayerbase plate 2 and a second face 74 b oriented towards the side of themultilayer base plate 2. An outwardly spread curve 75 is formed at asection where the first face 74 a and the overhang portion 72. Thespread curve is provided for allowing easy supply of an adhesive 70 intothe section to be bonded between the radome 7 and the multilayer baseplate 2. In addition, a groove 73 is formed in the face 74 a.

By putting the above-mentioned face 74 a to the surface of themultilayer base plate 2, a required design gap “d” can be accuratelysecured between the multilayer base plate 2 and the radome 7. After themultilayer base plate 2 and the radome 7 have been put to together, theadhesive 70 is charged into the section to be bonded between the baseplate 2 and the radome 7. At this time, even if the section to be bondedoverflows with the adhesive 70, the excess thereof is received into thegroove (adhesive gutter) 73. Accordingly, it makes possible to preventthe adhesive 70 from entering the millimetric-wave device, and thus toimprove product quality.

On one face of the radome 7, a connector 10 with external connectionterminals is formed integrally with the radome 7.

As shown in FIG. 3, a temperature sensor 300 is disposed on themultilayer base plate 2. Since the oscillator 20 for generating themillimetric waves could change in characteristics with temperature, thetemperature sensor 300 monitors a temperature state of the multilayerbase plate 2. Thus, an oscillation frequency of the oscillator IC ismonitored, the oscillation frequency is maintained by temperaturecontrol, and a warning is issued if a shift in the oscillation frequencyoversteps a predetermined range.

A longitudinal sectional view of a multilayer base plate 2 according toanother embodiment is shown in FIG. 7.

The multilayer base plate 2 in FIG. 7 has a plurality of heaters 203interposed between layers, and is adapted so that the uniformity oftemperature can be obtained. The heaters 203 are each set so as to becontrolled to a required temperature on the basis of a value detected bythe temperature sensor 300. To stabilize the characteristics of themillimetric-wave oscillator, temperature control and temperatureuniformity of the device itself of FIG. 1 are important. Amillimetric-wave frequency of 76.5 GHz, in particular, is required bythe Radio Law to stay between 76 and 77 GHz within a particularoperating temperature range.

In order to realize the above, the heaters 203 are formed inside themultilayer base plate 2 and function together with the foregoingtemperature sensor 300 to control temperature. The heaters 300 use apower supply voltage of 30-40 V to miniaturize a heater control IC.

In the embodiment of FIG. 1, the microcomputer 251, the DSP 252 andother electronic components are each coated with organic protectionresin 9 to ensure protection from moisture. Alternatively to suchcoating, however, even if, as shown in FIG. 4, an organic protectionresin 41 is charged into the space (except for the hermetically sealedsection 45) between the case 8 and the multilayer base plate 2, there isno problem in terms of characteristics.

Next, a manufacturing process for a major section (module) of themillimetric-wave radar device according to the present embodiment isdescribed below using FIG. 8.

A multilayer base plate 2 is formed by stacking in layer fashion aplurality of green sheets, each of which comprises a dielectric plate200, and then baking these elements with an electroconductive layer 20being interposed between layers. The electroconductive layer 201 isconstituted by a power supply layer, a ground layer for each powersupply, and other layers.

As shown in FIG. 8(a), on the multilayer base plate 2, via-holes 6 areformed and on the reverse side of the multilayer base plate 2, wiringpatterns 35 and cases 4 are formed.

Next, as shown in (b) and (c), a resin film 110 is formed on themultilayer base plate 2, then a metal film is formed on the resin film110, and patterning is provided to form antenna patterns 3. Next, asshown in FIGS. 8(d) and 8(e), a hole 120 is made in part of anelectroconductive section of the antenna patterns 3 and then anelectroconductive material 130 is charged into the hole 20 by sputteringor the like so that the antenna patterns 3 are connected to a via-hole6. After this, as shown in (f) to (h), an RF module chip 20, amicrocomputer 251, a DSP 252, and other electronic components are bondedto form an electric signal circuit. In addition, a cover 5 is bondedwith the cases 4 to form a hermetically sealed structure, and themicrocomputer 251, the DSP, and other bare chips are each coated withorganic protection resin 40.

During the above manufacturing process, antenna characteristics againstmillimetric waves are checked in the step shown in FIG. 8(g), i.e., in astep performed after the RF module 20 has been hermetically sealed(before other electronic components are mounted). In addition, totalinput/output characteristics are checked in a step performed after allelectronic components have been mounted on the multilayer base plate 2,as shown in FIG. 8(h).

According to the present embodiment, the following effects are obtained:

(1) Since the antenna patterns 3 and the electronic components forprocessing signals are integrally provided on the multilayer base plate3, it is possible to enhance component-mounting density and make thedevice more compact.

(2) Even if the oscillator, amplifier, and frequency converter forprocessing an antenna signals are constituted by a bare IC, by sealingthese electronic components hermetically for complete moistureprotection, the frequency characteristics of millimetric waves can beprevented from changing. The present embodiment provides a hermeticallysealed structure to the millimetric-wave oscillator and the frequencyconverter required to proof against severe moisture conditions, whereasprovides simplified resin coating to the microcomputer, DSP and otherbare-chip components loosened in terms of moisture-proofing conditions,compared with the foregoing components. Accordingly, the hermeticallysealed structure needed comparatively high-cost can be applied only tothe minimum necessary number of components, and a locally narrow spaceis sufficient for the installation space of the components required thehermetic seal. And the other electronic components not required a severehermetically sealed condition are arranged on the periphery of the abovesevere hermetically sealed components. It is therefore possible torealize the enhancement of component-mounting density and reduction incosts.

(3) By hermetically sealing only the millimetric-wave oscillator,amplifier, and frequency converter in a localized space andindependently of other electronic components, it is possible to test andcheck antenna characteristics prior to measuring and checking theinput/output characteristics of the entire device. Accordingly, if anydefective components are detected in this phase, an unnecessary waste ofcomponents can be avoided since it is possible to eliminate thedefective components before starting total component assembly.

(4) Since the device is constructed so that the design gap between theantenna unit and the radome can be easily controlled in terms ofmanufacturing dimensions, and by preventing the reflection ofmillimetric-wave output signals from the radome surface, it is possibleto enhance radar accuracy.

(5) Radar accuracy can be further enhanced by improving the mountingaccuracy of the millimetric-wave radar device.

Industrial Applicability

According to the present invention, circuits for generatingmillimetric-wave radar antenna signals and undertaking input/outputprocessing, and circuits for receiving and processing input signals canbe integrated and a compact, thin. Furthermore highly accuratemillimetric-wave radars can be provided at a low cost.

1. A vehicular millimetric-wave radar device comprising: an antenna unitfor sending out electromagnetic waves of a millimetric-wave band tooutside and receiving the wave reflected from a target; and a circuitfor signal-processing the reflected waves; wherein said radar devicefurther includes a multilayer base plate formed of a plurality ofstacked layers of dielectric plates and an electroconductive layerinterposed between each layer; said multilayer base plate has, on oneside, said antenna unit formed with a pattern, and on the other side, acircuit wiring pattern and electronic components for signal processingof millimetric waves; and among said electronic components, amillimetric-wave signal oscillator, an amplifier and a frequencyconverter are housed in a hermetically sealed section formed with alocal space on said multilayer base plate, and the other electroniccomponents are arranged in a non-hermetically structured condition onthe periphery of said hermetically sealed section.
 2. The vehicularmillimetric-wave radar device according to claim 1, wherein saidmillimetric-wave signal oscillator, said amplifier, and said frequencyconverter are hermetically sealed in an inert gas atmosphere, whereas atleast part of said other electronic components arranged in anon-hermetically structured condition is protected by resin coating. 3.The vehicular millimetric-wave radar device according to claim 1,wherein said multilayer base plate on which said antenna patterns, saidhermetically sealed section and said electronic components are mountedis covered with a plastic radome and an electroconductive case.
 4. Thevehicular millimetric-wave radar device according to claim 1, whereinsaid millimetric-wave signal oscillator, said amplifier, and saidfrequency converter are housed in IC form within said hermeticallysealed section.
 5. The vehicular millimetric-wave radar device accordingto claim 1, further comprising a plastic radome for covering the face ofthe antenna unit side on said multilayer base plate, and anelectroconductive case for covering the face of the electroniccomponents side on said multiplayer base plate; wherein said radome isbonded with said multilayer base plate to form a structure integratedtherewith; overhang portions protruding outwardly with respect to saidcase is formed on said radome; and holes for installing saidmillimetric-wave radar device are provided at said overhang portions. 6.The vehicular millimetric-wave radar device according to claim 1,further comprising a plastic radome for covering the face of the antennaunit side on said multilayer base plate; wherein overhang portionsprotruding outwardly is formed at both sides of said radome; anengagement portion engaging with the peripheral edge of said multilayerbase plate is formed at the inner edge of an opening in said radome;said engagement portion is formed of a first face put to the face of theantenna unit side of said multilayer base plate and a second faceadjoining the side of said multilayer base plate; an outwardly spreadcurve is formed at a section where said first face and said overhangportion intersect; a groove is formed at the first face; and saidmultilayer base plate is in engagement with the inner edge of theopening of said radome via an adhesive.
 7. The vehicularmillimetric-wave radar device according to claim 3, wherein said radomeis molded integrally with a connector having input/output terminals forconnecting external terminals.
 8. The vehicular millimetric-wave radardevice according to claim 1, further comprising a temperature sensor onthe surface or inside of said multilayer base plate.
 9. The vehicularmillimetric-wave radar device according to claim 1, further comprising aheater on said multilayer base plate, said heater being controlled at avoltage from 30 to 50V.
 10. The vehicular millimetric-wave radar deviceaccording to claim 1, wherein the distance between the inner surface ofsaid radome and the face of the antenna side of said multilayer baseplate is equal to an integer multiple of a wavelength of the millimetricwave.